(1) Field of the Invention
The present invention relates to a document feeder for use in an image forming apparatus including an image reading unit (scanner) with a document feeder for reading the image of originals, a recording unit (printer) for reproducing a visual image of image data, inclusive of the read image data, on a recording medium. More specifically, the present invention relates to a document feeder which enables easy handling of the documents to be read when the recording operation is stopped due to an anomaly on the recording unit side.
(2) Description of the Prior Art
A recording unit (printer) forms a visual image from the image data read from the image of an original, the image data supplied from other apparatus and the like, on a sheet as a recording medium, thus producing a hard copy. Typical examples of technologies for such recording devices includes the electrophotographic technique, the ink-jet technique whereby ink is selectively ejected for recording, the thermal-recording technique using a thermal head with a heat sensitive paper or heat transfer ink, and the like.
When such a recording apparatus has an image reading unit for reading the image of an original, i.e., a scanner, the apparatus not only performs a printing function as a printer, but also provides a reading function and a copying function by the combination of these.
A scanner performs the scanning function by illuminating, with light from a light source, a document placed on or as being conveyed along an original table, which is typically formed of transparent material such as glass etc., optically scanning the original, focusing the obtained, reflected light onto an optical receiver of a photoelectric transducer (reading element) such as CCD etc., and outputting an electric signal (analog signal) corresponding to the received amount of light. Then the analog signal is converted into a digital signal, which is output as the image data reproducible as a visual image.
When the recording apparatus for reproducing a hard copy from the above image data, or more simply a printer, is based on electrophotography, the printer performs its function or creates a hard copy by the steps of: charging the photoreceptor surface as an image support at a uniform surface potential; illuminating the photoreceptor with a laser beam from a semiconductor laser which is driven in accordance with the image data so as to form a latent image; and developing it with the toner and transferring the developed image (toner image) to a sheet.
When the printer is based on the ink-jet technology, the printer creates a hard copy with ink by the steps of: receiving the image data picked up by the aforementioned scanner etc., ejecting ink selectively from the ink ejection nozzle in accordance with the image data onto a recording medium (sheet). In a thermal recording method, heat generating elements arrayed in the thermal head are driven selectively to crate a hard copy on heat sensitive paper as a recording medium or to create a hard copy by fusing ink on the ink ribbon and transferring it to a sheet.
Here, in order to optically scan the original, the aforementioned scanner makes a carriage incorporating a light source and reflection mirrors etc., for illuminating the original on the original table, travel in parallel with the original table and focusing the reflected light on the CCD photo-receiving surface as a reading device by means of a focusing lens, so as to read the image of the original, line by line, or a group of lines at a time.
In such an image forming apparatus, while the original documents to be read are conveyed, recording media, i.e., print sheets should be conveyed to the image forming station (recording position) for image formation. During this operation, if a sheet jam occurs on the recording unit side, the operation of the recording unit is stopped and the operation of the scanner side is also stopped at the same time. After the jam cancellation on the recording unit side, the originals should be rearranged on the scanner side conforming to the jam handling.
In this case, instead of replacing all the documents to the initial placement, the user needs to perform troublesome work to sort out the unfinished documents from the finished documents by checking where image forming has been completed, with reference to the jammed sheet.
In order to eliminate such a trouble task, conventionally, conveyance of the originals is controlled continuously without stopping the operation on the scanner side so as to ease the user's document handling even when a paper jam occurs on the recording unit side. For example, Japanese Patent Application Laid-Open Hei 5 No.11523 discloses a configuration in which the documents which have started to be conveyed from the document tray are all discharged by force to the discharge tray. This configuration makes it unnecessary for the user to open the conveyance path to collect the documents therefrom. Thus, the handling step is simplified.
Japanese Patent Application Laid-Open Hei 11 No.15210 discloses a configuration in which once jamming occurs on the recording unit side, it is checked where the document under conveyance is located and whether reading of the document has been finished, based on the sensor arranged in the document conveyance path or at the document reading station, and after the jam cancellation, the document is force-discharged and it is determined based on the above judgement whether the discharged document should be re-fed, to thereby display the judgement result. According to this configuration, the user is able to know if the force-discharged document needs to be read again based on the display content whilst the user is handling the jammed sheet and can, based on this knowledge, sort out the document to be replaced to the document tray.
In contrast, Japanese Patent Application Laid-Open Hei 3 No.182478 discloses a document feeder of a document circulation type in which once jamming occurs on the recording unit side, the document feeder is driven in reverse so as to send back the document on the document conveyance path to the document tray. In accordance with this configuration, the user only needs to remove the jammed sheet while the document feeder selectively controls and feeds again the sent back document from the image forming apparatus to the reading station.
In the above ways, instead of stopping the conveyance of the document on the scanner side at once when paper jam occurs on the recording unit side, some or several document feed manipulations have been devised so as to ease the user's document handling under the consideration of the handling after jam cancellation.
However, force-discharging of documents only elides the removal work of the documents present in the document conveyance path but cannot eliminate the job of replacing the discharged documents to the document tray. In this case, even when the user is informed of the documents to be replaced via the display device, the user may by mistake return the documents to those in the document tray in a wrong manner. For example, the documents should be returned conforming to the delivery configuration, or whether documents are delivered from the topmost or lowermost of the document tray. If the documents are returned without considering the delivery configuration, the order of the documents may be disturbed.
Therefore, if the apparatus is configured so that the documents once delivered from the document tray can be sent back to the document tray, the replacement job of the documents which would have been done by the user can be omitted. However, since the documents need to be conveyed in the reverse direction, the documents tend to jam more easily during reverse conveyance. Actually, when a document is conveyed in the direction opposite to that up to that point, the document may become stuck in the conveyance path due to its setting, curvature and the like. In order to avoid this, the conveyance path should be designed taking into consideration the reverse conveyance. This reduces the design flexibility of the conveyance path. In particular, since the conveyance path is usually designed so that the sheet is conveyed in a predetermined direction, giving consideration to the reverse feed direction will strongly limit the design.
Further, to send the documents back to the document tray, it is necessary to classify the documents depending upon the readout situations, that is, those after being read, those still being read, those before reading and idly circulate the document after being read through the reading station. Therefore, it takes time for the start of reading. Moreover, since, in order to send the document back to the document tray, the document which was delivered out before for being read need to be sent out from the beginning again, the system needs the time up to the first reading for initialization.
Moreover, in a configuration where the document after being read is discharged by, particularly, circulation conveyance, if the documents are fed from the topmost or lowermost, the document after being read is sent back to the topmost or lowermost. Therefore, if an image formed sheet corresponding to the document after being read has not be discharged and becomes stuck, the document needs to be fed to the reading station first. The user needs to collate the documents or performance of idle circulation can deliver the document to the reading station. In this case, such idle circulation is needed, and this not only needs a considerable time before reading but also increases the likelihood of damaging other documents.
In order to solve the above drawbacks, Japanese Patent Application Laid-Open Sho 60 No. 8865 discloses a configuration. In this invention, a suctioning and conveying means is provided above the tray. That is, when the document with its image completely read out is discharged to the discharge tray (the document tray based on document circulation), the document is held in its discharged state by the suctioning and conveyance means instead of being discharged onto the tray. Then, the sheet having the image of the document recorded thereon is discharged, the document being held by the suctioning and conveying means is discharged. If the sheet with the image recorded thereon is not discharged, the document being held is re-circulated by the suctioning and conveying means in order to read the document again. A special, separate conveyance path leading the document to the reading station is arranged at the suctioning and conveying means.
In this configuration, since the document has not been discharged when a sheet jam occurs on the recording unit side, the document can be re-fed to the reading station, thus making it unnecessary for the user to handle the original.
Nevertheless, as a means for holding the document before the determination of whether the document is to be discharged or not, extra suctioning and conveying means and a recirculating path through which the document passes to the reading station are required, resulting in a bulky and complicated configuration. Further, since the suctioning and conveying means is arranged over the document tray, this makes it very troubles some to place the documents to the document tray and remove them therefrom. That is, the suctioning and conveying means should be arranged to be openable with respect to the document feeder.